The present invention relates generally to machine vision vehicle service systems configured to measure parameters associated with one or more wheel assemblies on a vehicle, and more particularly, to a vehicle service system and methods for acquiring and processing image data representative of a three-dimensional region of a tire tread surfaces associated with a vehicle wheel assembly to provide an operator with information related to the condition of the tire tread.
It is well known that the condition of the tires of a motor vehicle, and in particular, the condition of the tire tread, can have a significant impact on the performance of the vehicle as well as be indicative of potential problems with the vehicle. For example, tires with excessive tread wear lack the ability to evacuate water from the contact patch region when traveling over wet road surfaces, leaving the vehicle dangerously susceptible to hydroplaning and a loss of control. Uneven tread wear across the width of a tire's outer surface may be indicative of an improper wheel alignment or a broken component in the vehicle suspension system. Improper inflation of a tire can result in the failure of the tire to properly support the vehicle, leading to bulges in the tire sidewall adjacent to the contact patch, and excessive fuel consumption by the vehicle.
A number of measurement systems for obtaining a measure of tire tread depth for a motor vehicle wheel at a limited number of discrete points or locations about the tire circumference are known. For example, U.S. Pat. No. 7,797,995 B2 to Frank H. Schafer discloses a device for detecting a profile depth and/or profile type of a motor vehicle wheel traveling in a straight line, at a constant speed, over a narrow-width sensor embedded in a roadway surface. A laser is scanned across the exposed segment of the tire, and images acquired which are processed to evaluate the tire profile depth and type at the observed location. However, the design of the '995 system limits the measurement of profile depth and type to a very small sliver of the tire, which is visible for the brief moment when the tire passes directly over the embedded sensor.
International patent application WO 2010/115390 to Ulrich Pingel sets forth a system for measuring the tread depth of a vehicle tire where the profile of the tire is observed across one measuring line by a laser or light emanating from a light source in a fan beam pattern, and which is reflected back to a sensor. The signal of the reflected fan beam is evaluated using a triangulation method to determine a measure of the tire tread depth across the illuminated line of the tire surface.
U.S. Pat. No. 6,789,416 B1 Tracy et al. sets forth a tire tread scanner configured to be positioned against a tire tread surface, and which utilizes a laser scanner to scan a laser transversely across the tread surface while measuring the range between the emitter and the tire tread surface, thereby producing a two-dimensional profile of the tire tread at the position of the scanner.
A similar laser scanner for measuring tire tread depth across the width of a tire is shown in International patent application WO 2010/100417 A2 to Pryce et al, and employs a laser line generate to generate an elongate pattern of light which is reflected onto the surface of a tire. Reflected light from the tire is then acquired at an associated camera to obtain a linear image of the illuminated tire tread.
While many of the known systems for measuring tire tread depth employ optical scanning technology to acquire tire tread depth data, the data is acquired across a very limited portion of the tire tread, often limited to a single linear scan across the tire surface. Other prior art systems use only a few linear scans of tire tread depth data, thus lacking a means to provide an accurate representation of the tire tread wear or characteristics over a region on the tire surface or over the entire circumference of the tire. Such systems vary in accuracy depending upon the particular portion of a tire tread pattern which is imaged by the linear scan.
Yet other prior art systems that may obtain enough data to construct a point-cloud do not take full advantage of the additional data, and still try to identify only particular grooves or specific locations on the tire where tread-depth is determined (i.e., in a groove near the inner edge, in a groove near the middle of the tire, and in a groove near the outer edge), thereby ignoring most of the acquired data.
Accordingly, there is a need in the automotive service industry to provide both a vehicle operator and a vehicle service technician with information regarding the condition of the tires mounted to a vehicle, including a measure of the tire tread depth and contact patch parameters over an entire region or circumferential surface of the tire. There is further a need in the automotive service industry to provide an accurate and repeatable measure of tire tread wear and tire condition which accommodates the changes in a tire tread pattern within the observed region on the tire surface and which can be tolerant of the presence of tire damage and/or foreign object embedded within the tire tread pattern.
There is a further need in the automotive service industry to provide an improved method for displaying to an operator tire tread depth data acquired over a region of the tire surface. Systems which provide the operator with a two-dimensional or three-dimensional image often rely exclusive on a spectrum of colors to indicate the depth of the tire tread at various points. While such displays are visually interesting to an operator, they are actually difficult to use when trying to determine a tread depth measurement at a specific point within the observed region, as the operator must determine exactly what color corresponds with each measurement in the region of interests.
Accordingly, it would be beneficial to provide an operator with an annotation or other indication in the two-dimensional or three-dimensional image of the tire tread depth which is associated with a specific numerical value of the measured tire tread depth at that point or over a selected region. It would be further advantageous to enable an operator to selectively reposition the focus of the annotation or other indicator within the two or three-dimensional image to view a numerical representation of measured tread depth at a different selected position or region on the tire surface. Finally, it would be advantageous to provide an operator with a means to selectively view or highlight those portions of a two or three-dimensional image which illustrate portions of a tire tread having a depth equal to, or less than, a selected numerical value.
Tire tread depth, as an indication of tire wear, is but one indicator of the overall state of a vehicle, and can be influenced by a number of factors, including tire pressure, operator driving style, wheel alignment settings, and suspension components. Accordingly, it would be advantageous to provide a method for illustrating the interactive effects of one or more of these indicators on a two or three-dimensional image of tire tread depth over time. It would be further beneficial to provide a method by which identified problems in other areas of the vehicle, for example, a vehicle's wheel alignment, can be used to direct an operator's attention to specific features or trends observed in measurements of remaining tire tread depth.